Defrost spinach completely. Drain and squeeze dry spinach. Place spinach in a bowl and blend in salt, pepper, horseradish, and sour cream. Roll out pastry shell and put in 10-inch quiche pan. Spread the mixture in the pastry shell. Saute the mushrooms in butter then drain and layer on top of the spinach mixture. Sprinkle with the Parmesan cheese and then grated cheese. You can cover and refrigerate quiche shells overnight. In the morning beat the eggs and add the half and half, and other seasonings – beat until smooth. Pour the egg mixture into the pastry shell. Bake at 375 degrees in a preheated oven for 40 minutes or until the top is puffed up, browned and a knife inserted in the center comes out clean. Remove from the oven and let stand for 5 or 10 minutes to set. Serves 5 or 6 depending on how big you want your pieces.